Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $112.58   8.370%   $122.0029   $122.00   $122.00   $122.00  
  Purchase #2 $207.71   12.629%   $233.9417   $233.94   $233.95   $233.90  
  Purchase #3 $137.38   12.497%   $154.5484   $154.55   $154.55   $154.50  
  Purchase #4 $232.26   4.751%   $243.2947   $243.29   $243.30   $243.30  
  Purchase #5 $48.51   5.345%   $51.1029   $51.10   $51.10   $51.10  
  Purchase #6 $146.97   3.271%   $151.7774   $151.78   $151.80   $151.80  
  Purchase #7 $248.25   10.185%   $273.5343   $273.53   $273.55   $273.50  
  7 purchase totals = $1,133.66       $1,230.2023   $1,230.19   $1,230.25   $1,230.10